T-10 and muncie gear oil formula changing

[Tom I.]

I just bought a quart of NAPA Premium 80W-90 Gear oil. The instructions state "not for use in manual transmissions with synchronized gears. A friend make a couple calls and was told the latest oil formula will harm the brass syncro rings.
Has anyone heard of this problem and if so, is there Hypoid oil available that is syncro friendly? I have older GL5 type NAPA gear oil that does not have the non-use statement.
Tom I.

[Loren L.]

Re: T-10 and muncie gear oil formula changing

Well, take it back and return it. Let them know that you're a separate market.

[Frank D.]

Re: T-10 and muncie gear oil formula changing

Why not use the API-GL4 and be done with it ???

[Jim D.]

Re: T-10 and muncie gear oil formula changing

Use readily available GL-5 oil and don't believe the internet experts. Go to the 11:20 mark in this video for the REAL facts. https://www.youtube.com/watch?v=Z7NpsMZ9pBQ

[Frank D.]

Re: T-10 and muncie gear oil formula changing

And 20 minutes in he states that he personally uses Driven GL-4....
I'll try to find some...

[Jim D.]

Re: T-10 and muncie gear oil formula changing

That's what he prefers in his racing transmissions. I couldn't find it and Paul told me that any GL-5 is fine and you'd never be able to tell the difference on the street anyway. The purpose of my post was to dispel all the internet B.S. about GL-5 causing synchro failures.

[Tom I.]

Re: T-10 and muncie gear oil formula changing

I purchased and used NAPA type GL5 several years ago. The description on the container did not provide any restrictions pertaining involving the syncro rings. The NAPA type GL5 oil purchased recently did have the "do not use" restriction. My transmission has had GL5 type oil in it for several years not knowing of the restriction. The question is how much damage if any exists in my transmission over the last three years. Was GL5 oil formula changed or was the need for a restriction discovered after using GL5 for some time.
GL4 is still available with the statement "not corrosive to copper, bronze or other non-ferrous alloy bearings and bushings".
I will be replacing out GL5 with GL4 and purchasing extra GL4 for use down the road.
I do not recall reading information on this problem. If I have provided any incorrect information, please correct me.
Tom I.

[Tom I.]

Re: T-10 and muncie gear oil formula changing

Why has the label on NAPA GL5 oil container been recently changed to include "non-synchronized manual transmissions if this is not an issue?
For racing applications, damage do to time is not an issue but when transmissions are installed in these old cars time may be an issue.
Tom I.

[Jim D.]

Re: T-10 and muncie gear oil formula changing

I recently rebuilt my Muncie and the GL-5 I picked up locally had no such warning. I've been using GL-5 in transmissions for probably 20 years without issue. In the video, Paul stated he contacted the oil manufacturers and engineers and was told that if the oil was brought to a boiling temp. (which it never even gets close to in the trans.) it can cause the brass to tarnish/discolor. This tarnish has no effect on the performance of the synchro at all. He has built 1000's of transmissions and literally wrote the book on building them. I would think that after buying a $1000 worth of parts from him for my trans., he wouldn't tell me it's okay to run GL-5 if it were not true. That being said, use whatever makes you feel better.

[Jim D.]

Re: T-10 and muncie gear oil formula changing

For some reason, I can't edit my above post to include this but - this is the label on the generic GL-5 I just purchased. In fact, none of the several different brands of GL-5 had any warning about synchros.

[Duke W.]

Re: T-10 and muncie gear oil formula changing

The first thing to remember is that modern "manual transmission oils" are designed for modern manual transmissions, NOT MANUAL TRANSMISSIONS DESIGNED PRIOR TO 1970.

The original spec for manual transmissions and axles was Mil-L-2105D. If you don't believe me look in your owners and service manuals.

The mil-spec was superseded by the commercial API 80W-90 GL-5 spec in the seventies and even the military canceled the mil-spec and uses the commercial API spec.

The "yellow metal corrosion" story is a myth. It can happen, but only at temperatures well above the operating temperature of any manual transmission. Neither I nor anyone I have ever discussed this issue with, including some who have spent years overhauling vintage manual transmissions, have ever seen synchronizer corrosion... wear, yes, corrosion, NO!

This new warning label is likely just a CYA effort in case some bozo decides to put GL-5 in a modern manual transmission. The fact of the matter is that oil blenders don't give a flying f... about designs that date back 50-70 years, but they do worry about lawsuits from owners of modern cars that use the wrong oil.

Duke

[Allen N.]

Re: T-10 and muncie gear oil formula changing

I have been reading about gear oils for the last two hours and decided I would use Sta-Lube 80W-90 GL-4 in my 1970 Muncie I am about done rebuilding. All I can find on the internet is Sta-Lube 85W-90 GL-4. I am thinking it should be fine, but what is your opinion on using the 85W-90?
Thanks,
Allen

[Duke W.]

Re: T-10 and muncie gear oil formula changing

My recommendation for vintage manual transmissions is the modern equivalent of the old Mil-L-2105D that was originally specified, which is 80W-90 GL-5.

If it works, don't fix it.

Duke